Encoder including an origin position detection function

Abstract

An encoder includes a scale having a continuous part where physical characteristics varies and a discontinuous part that interrupts the continuous part, a detector that be relatively displaced with respect to the scale and that detects the physical characteristics of the scale, and a processor that detects an origin of the scale on the basis of a signal for displacement detection output from the detector. The detector includes a sensitive part having sensitivity contributing to the signal for displacement detection and an insensitive part having no sensitivity contributing to the signal for displacement detection. The processor detects the origin on the basis of signal intensity of each of signals for displacement detection that the detector outputs when the sensitive and insensitive parts detect physical characteristics of the discontinuous part.

What is claimed is: 
     
       1. An encoder comprising:
 a scale including a continuous part where physical characteristics periodically varies, and a discontinuous part that interrupts the continuous part; 
 a detector that is relatively displaced with respect to the scale and that detects the physical characteristics of the scale; and 
 a processor that detects an origin of the scale on the basis of a signal for displacement detection output from the detector, 
 wherein the detector includes a sensitive part having sensitivity contributing to the signal for displacement detection on the basis of the physical characteristics and an insensitive part having no sensitivity contributing to the signal for displacement detection on the basis of the physical characteristics, and 
 wherein the processor detects the origin on the basis of signal intensity of the signal for displacement detection when the sensitive part detects physical characteristics of the discontinuous part and on the basis of signal intensity of the signal for displacement detection when the insensitive part detects the physical characteristics of the discontinuous part. 
 
     
     
       2. The encoder according to  claim 1 , wherein a length of the sensitive and insensitive parts along a displacement direction of the scale is longer than a length corresponding to a wavelength of the continuous part in the detector. 
     
     
       3. The encoder according to  claim 1 ,
 wherein the sensitive part includes a first, a second and a third sensitive parts, and the insensitive part includes a first and a second insensitive parts, 
 wherein the first sensitive part, the first insensitive part, the second sensitive part, the second insensitive part and the third sensitive part are placed in order from a first end in a displacement direction of the scale, and 
 wherein the processor detects the origin on the basis of signal intensity of a signal that the detector outputs when either of the sensitive parts arranged at both ends of the detector detects the physical characteristics of the discontinuous part and on the basis of signal intensity of a signal that the detector outputs when the insensitive part adjacent to the either of the sensitive parts detects the physical characteristics of the discontinuous part. 
 
     
     
       4. The encoder according to  claim 1 , wherein the processor calculates differences between a maximum signal value and a minimum value of signal values for a length corresponding one wavelength of the continuous part in the detector as signal intensity using the signal for displacement detection. 
     
     
       5. The encoder according to  claim 1 , wherein the processor calculates a square sum of at least two phase signals for displacement detection as signal intensity. 
     
     
       6. The encoder according to  claim 1 ,
 wherein the processor includes a counter that counts number of signals output from the detector, and 
 wherein the counter updates the number of signals to a predetermined value when the processor detects the origin. 
 
     
     
       7. The encoder according to  claim 1 , wherein the encoder is a linear encoder. 
     
     
       8. The encoder according to  claim 1 , wherein the encoder is a rotary encoder. 
     
     
       9. An apparatus comprising an encoder,
 wherein the encoder includes:
 a scale including a continuous part where physical characteristics periodically varies and a discontinuous part that interrupts the continuous part; 
 a detector that is relatively displaced with respect to the scale and detects the physical characteristics of the scale; and 
 a processor that detects an origin of the scale on the basis of a signal for displacement detection output from the detector, 
 
 wherein the detector includes a sensitive part having sensitivity to the physical characteristics contributing to the signal for displacement detection and an insensitive part having no sensitivity to the physical characteristics contributing to the signal for displacement detection, and 
 wherein the processor detects the origin on the basis of signal intensity of the signal for displacement detection when the sensitive part detects physical characteristics of the discontinuous part and on the basis of signal intensity of the signal for displacement detection when the insensitive part detects the physical characteristics of the discontinuous part. 
 
     
     
       10. The apparatus according to  claim 9 , wherein a length of the sensitive and insensitive parts along a displacement direction of the scale is longer than a length corresponding to a wavelength of the continuous part in the detector. 
     
     
       11. The apparatus according to  claim 9 ,
 wherein the sensitive part includes a first, a second and a third sensitive parts, and the insensitive part includes a first and a second insensitive parts, 
 wherein the first sensitive part, the first insensitive part, the second sensitive part, the second insensitive part and the third sensitive part are placed in order from a first end in a displacement direction of the scale, and 
 wherein the processor detects the origin on the basis of signal intensity of a signal that the detector outputs when either of the sensitive parts arranged at both ends of the detector detects the physical characteristics of the discontinuous part and on the basis of signal intensity of a signal that the detector outputs when the insensitive part adjacent to the either of the sensitive parts detects the physical characteristics of the discontinuous part. 
 
     
     
       12. The apparatus according to  claim 9 , wherein the processor calculates differences between a maximum signal value and a minimum value of signal values for a length corresponding one wavelength of the continuous part in the detector as signal intensity using the signal for displacement detection. 
     
     
       13. The apparatus according to  claim 9 , wherein the processor calculates a square sum of at least two phase signals for displacement detection as signal intensity. 
     
     
       14. The apparatus according to  claim 9 ,
 wherein the processor includes a counter that counts number of signals output from the detector, and 
 wherein the counter updates the number of signals to a predetermined value when the processor detects the origin. 
 
     
     
       15. The apparatus according to  claim 9 , wherein the encoder is a linear encoder. 
     
     
       16. The apparatus according to  claim 9 , wherein the encoder is a rotary encoder.